1. Field of the Invention
This invention relates to maintenance termination units for telecommunications systems.
2. Description of Prior Art
In modern telecommunications systems, a line of demarcation exists between the telecommunications network owned and maintained by the provider and the customer premises equipment owned and maintained by the customer. A maintenance termination unit (MTU) is a circuit commonly used to determine whether any defects reside in the network or in the customer equipment. Basically, the unit comprises bidirectional switches which are activated by a predetermined voltage and current level on the lines in order to disconnect the customer equipment from the network. If the fault persists after the customer has been disconnected, the problem lies in the network. (See, for example, U.S. Pat. No. 4,396,809 issued to Brunssen, and U.S. Pat. No. 4,529,847 issued to DeBalko.) In some earlier types of MTUs, a relay was used to connect a relaxation oscillator across the lines for testing. (See U.S. Pat. No. 4,054,759 issued to McGrath et al.)
In some instances, for example when a customer installs equipment which does not meet standards for the network, the presence of the MTU can cause the equipment to malfunction. Also, in some systems, such as Integrated Services Digital Network (ISDN), the MTU may not be compatible with the standard signaling on the lines. In such cases, it is desirable to be able to disconnect the MTU from a remote location and reconnect it when it is desired to test the system.